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Old 09-03-2007, 05:00 PM   #1
TJ213
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I am currently working on a small electric vehicle, and need a transmission. At this point I am trying to research snowmobile transmissions, and have a few questions.

1- Where can I find snowmobile transmissions
2- What do they need as far as oil, trans fluid, control, etc.
3- What is the powerband of most transmissions (where do they keep the RPMs?)
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Old 09-03-2007, 05:33 PM   #2
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Snowmobiles operate on a pair of infinitely adjusting torque/RPM sensing pulleys. The front pulley (or primary/drive clutch) is attached to the crankshaft of the engine. The rear pulley (secondary or driven clutch) is attached to either a jackshaft/chaincase or to the driveline that drives the track. The front pulley drives the rear pulley through a belt. There are no gears or gearcase in the "transmission" system. To develop a snowmobile CVT system to an electric vehicle, the output shaft of the motor will have to match the taper of the primary pulley (clutch), and your final drive would have to adapt to the size of the secondary pulley (clutch).

Both pulleys (clutches) are tapered where the belt rides. The belt rides low in the front clutch and high in the rear clutch. That gives you the greatest gear multiplication and low gear ratio for ease of starting. The front clutch is held open by a spring. The rear is held closed by a spring. As the engine RPM spins the front clutch, flyweights force one side (movable sheave) of the clutch toward the other, emparting force on the side of the belt. The belt initially will slip, but as more RPMS are added, the belt squeezes tighter, making the rear pulley move, which moves the jackshaft or driveshaft. As more RPM are added, the belt moves higher in the front clutch and lower in the rear clutch. At max RPM, the belt will be near the outer edge of the front clutch and almost in the center of the rear clutch, giving highest gear ratio for top speed. Most clutches are designed to run on a 1:1 ratio, but there are a few that actually overdrive.

Clutching on a snowmobile is done to the desired engine RPM. If the engine makes it's power at a certain RPM, that is where the clutching is set. On a 2-stroke, going past the powerband means losing power, sometimes substantially. There are many spring/flyweight combinations to set the RPM so that the engine is operating at the most efficient RPM. When you modify components in the engine, you also have to modify the clutching to accomodate the change in powerband.

A good resource for you to look at would be Olav Aaen's book "Clutch Tuning Handbook". It will give you a lot better understanding on how the CVT system on a snowmobile works, and how you can develop the technology for an electric motor and your intended application.

Good luck, when you get it done, post some pics!
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Old 09-03-2007, 05:42 PM   #3
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This is a picture of the two clutches on my 2002 800 RMK

[attachment=38277:IMG_1634.JPG]
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Old 09-03-2007, 08:12 PM   #4
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you can also get smaller clutches such as a " comet torqe converter " that is similar in design but on a smaller scale for less powerfull applications or a simple centrifical clutch
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Old 09-04-2007, 12:05 AM   #5
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Quote:
I am currently working on a small electric vehicle, and need a transmission. At this point I am trying to research snowmobile transmissions, and have a few questions.

1- Where can I find snowmobile transmissions
2- What do they need as far as oil, trans fluid, control, etc.
3- What is the powerband of most transmissions (where do they keep the RPMs?)[/b]
Being the curious kinda guy that I am, why in the world would you need a CVT or any ratio changing transmission with an electric motor? With max torque available almost as soon as the motor starts to turn, I always thought a transmission was not needed. I guess if your working on a hybrid, then disregard my question.

1. where, Comet Industries, Richmond Indiana, and no I don't know their website( or snowmobile junkyards)

2. no oil, no fluids, springs and weights and ramps

3. most snowmobile CVT's run 4,000 to 8,000 rpm.
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Old 09-04-2007, 08:45 AM   #6
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Being the curious kinda guy that I am, why in the world would you need a CVT or any ratio changing transmission with an electric motor? .[/b]

For different speeds. I'm pretty sure that he doesn't want to be going full speed as soon as the motor is turned on...
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Old 09-04-2007, 10:59 AM   #7
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Quote:
For different speeds. I'm pretty sure that he doesn't want to be going full speed as soon as the motor is turned on...[/b]
OK, OK, consider the following;

On an IC engine, you need an engine speed controller ( that would be the buttefly valve in your carb or throttle body), a torque mutiplying transmission ( could be a CVT or a "Muncie Rock Crusher" 4-speed) and some kind a clutch mechanisim in order to get a vehicle to start movement down the road or trail and control vehicle speed.

On a electric motor, you need a motor speed controller ( on small motors, usually some kind of variable resistor, old fart like me, think rheostat. 10 amp to 200 amp motors, well now your talking some kind a sophisticated solid state controller. Want most of those valuable watts to go to forward motion, instead of heat, well that's where smart electrical engineers are making the big bucks designing highly effecient motor controls.) That's it. As I said before, max torque is available on a electric motor from 1 rpm to 2000 rpm, so no conventional transmission needed, nor clutch. The electric motor control also controls vehicle speed. Yeah, you may want some kind of final drive ratio to match max motor speed to desired max vehicle speed, and maybe adjust for vehicle weight, but direct drive is probably the way to go.

At least that's what I learned at the Holiday Inn Express last night.
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Old 09-04-2007, 11:52 AM   #8
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At least that's what I learned at the Holiday Inn Express last night. [/b]
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Old 09-04-2007, 12:01 PM   #9
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Nicely done there Mr. Snofast.......

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Old 09-04-2007, 02:01 PM   #10
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Quote:
OK, OK, consider the following;

On an IC engine, you need an engine speed controller ( that would be the buttefly valve in your carb or throttle body), a torque mutiplying transmission ( could be a CVT or a "Muncie Rock Crusher" 4-speed) and some kind a clutch mechanisim in order to get a vehicle to start movement down the road or trail and control vehicle speed.

On a electric motor, you need a motor speed controller ( on small motors, usually some kind of variable resistor, old fart like me, think rheostat. 10 amp to 200 amp motors, well now your talking some kind a sophisticated solid state controller. Want most of those valuable watts to go to forward motion, instead of heat, well that's where smart electrical engineers are making the big bucks designing highly effecient motor controls.) That's it. As I said before, max torque is available on a electric motor from 1 rpm to 2000 rpm, so no conventional transmission needed, nor clutch. The electric motor control also controls vehicle speed. Yeah, you may want some kind of final drive ratio to match max motor speed to desired max vehicle speed, and maybe adjust for vehicle weight, but direct drive is probably the way to go.

At least that's what I learned at the Holiday Inn Express last night. [/b]
the electric powered drag cars I have seen have the motor control for motor speed but also have a powerglide (2 speed chevy trans) behind the motor.
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